Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.89	12.722%	$273.7905	$273.79	$273.80	$273.80
Purchase #2	$159.92	3.706%	$165.8466	$165.85	$165.85	$165.80
Purchase #3	$202.85	5.367%	$213.737	$213.74	$213.75	$213.70
Purchase #4	$199.83	3.753%	$207.3296	$207.33	$207.35	$207.30
Purchase #5	$77.79	5.800%	$82.3018	$82.30	$82.30	$82.30
Purchase #6	$75.96	3.423%	$78.5601	$78.56	$78.55	$78.60
Purchase #7	$175.59	7.362%	$188.5169	$188.52	$188.50	$188.50
7 purchase totals =	$1,134.83		$1,210.0825	$1,210.09	$1,210.10	$1,210.00